Effect of Zayandehrood River drying on Najafabad aquifer oscillations during past two decades

The study of changes in groundwater resources of Najafabad is an important issue for water resources management، especially after drying of Zayandehrood River. In the present study trend analysis conducted on groundwater level of 33 piezometeric stations located in Najafabad plain during 1374-1391 using Mann-Kendall non-parametric test. The slope of trend line was estimated by the Sen’s estimator method for each time series. Homogeneity of trends was tested using the Van Belle and Hughes method. Results showed that trends of groundwater level for all stations (except stations located out of drainage and irrigation networks) were significant negative. Significant negative trends exhibited for above 52 percent of stations. Results of trend line slopes revealed that in average groundwater level of Najafabad plain declined about 32 cm/year. The strongest decline belonged to Kahriz-sang-jadid station، which declined about 5. 92 m/year. Results of homogeneity of trends showed that trends were homogeneous for months، but it was heterogeneous for stations. Results of trend maps showed that the maximum level of groundwater changes occurred on drainage and irrigation network range. The isopiz maps showed that some stations located on the drainage and irrigation network range had declined about 50 to 100 meters in recent 17-years.